What is the ideal crop for a headshot?
Keep in mind some basic logic. The larger the image, the greater the impression the image makes on a web page. The larger the “item” in the image the greater the impact that “item” has in the image.
For example: If the image is filled with just a person’s face from chin to the crown of the head, the mouth will take up a large percentage of the image and will be noticed more and therefore will have a greater impact. This might be good for a tooth paste commercial.
However if the image has a person standing alone in a large room, the room will be noticed more and the room will have more (perhaps greater) impact than the person. This might be good for a decorating magazine.
So it really depends on the message your want to send.
If you want to tell the most about the person and their personality and you want to connect with them, the answer is in the eyes.
A formula I have come up with is that the head is about 50% of the image so that you are not too “in your face”. The body then sets the stage for the head. The eyes then can be about 1/3 of the way down which is considered the focal point in photography. And really the eyes are the way we communicate with people or connect with them. Also you are not showing so much body that the person looks our of balance or overweight.
Still in the end, the route depends on the use of the image, the message you want to send and personal taste.